WO2007057695A1

WO2007057695A1 - Improved spacer

Info

Publication number: WO2007057695A1
Application number: PCT/GB2006/004311
Authority: WO
Inventors: Howard Bradfield; Mussa Mahomed
Original assignee: Nylacast Ltd
Current assignee: Nylacast Ltd
Priority date: 2005-11-19
Filing date: 2006-11-20
Publication date: 2007-05-24
Anticipated expiration: 2008-05-19
Also published as: GB2446102B; GB0523599D0; GB0809605D0; GB2446102A

Abstract

A pipe in pipe spacer (10) for use in coaxial spacing a first pipe within a second pipe, for example, an oil pipe within a carrier pipe. The spacer (10) has an inner face (2) which contacts and engages with the outer surface of the first pipe and an outer surface (3) which contacts the carrier pipe. The inside face (2) of the pipe in pipe spacer (10) is coated with a coating (8) relatively of a soft deformable material, such as zinc, so that the coefficient of friction between the outer surface of the first pipe and the inside face of the pipe in pipe spacer is higher than the coefficient of friction between the outer surface of the first pipe and the inside face of the uncoated pipe in pipe spacer.

Description

Title: Improved Spacer

The present invention relates to an improved spacer, and in particular to an improved pipe in pipe spacer, for use in the co-axial spacing of, for example, an oil pipe within a carrier pipe as is commonly used in some offshore applications.

Pipe in pipe constructions are well known in the offshore industry as is the use of spacers, for example made from cast nylon, to co-axially space one pipe within another, for example an oil pipe within a carrier pipe. In use a plurality of such spacers are located along the length of the oil pipe at predetermined intervals. Typically the oil pipe has an outer surface of steel or fusion bonded epoxy, andinassemblytheoilpipeispuUedintothecarrierpipe. The carrier pipe typically also has an inner surface of steel.

In order to enhance the efficiency of construction the spacers should adhere to the inner pipe (oil pipe) and slide within the outer pipe thus maintaining the predetermined spacing. It is a disadvantage of known pipe in pipe spacers made from cast nylon that the coefficient of friction between the inside face of the cast nylon spacer and the outer surface of the oil pipe is relatively low, typically of the order of 0.3 where the pipe has an outer surface of steel. This means that, as the oil pipe, with spacers located at predetermined intervals, is pulled into the carrier pipe, there can be relative movement of the pipe in pipe spacer and the oil pipe altering the spacing between adjacent spacers and detracting from the construction. The extent of this movement will depend on the relative tightness of the fit of the spacer with respect to the respective pipe.

It is an object of the present invention to provide a pipe in pipe spacer in which the above disadvantages are reduced or substantially obviated.

The present invention provides a pipe in pipe spacer for use in the coaxial spacing of a first pipe within a second pipe, which pipe in pipe spacer has an inner face which contacts and engages with the outer surface of the first pipe, characterised in that the inside face of the pipe in pipe spacer is coated with a coating of a material so that the coefficient of friction between the outer surface of the first pipe and the inside face of the pipe in pipe spacer is higher than the coefficient of friction between the outer surface of the first pipe and the inside face of the uncoated pipe in pipe spacer.

The spacer according to the invention is typically a cast nylon spacer and is preferably coated with a metal or metal alloy or metal composite coating. Specific examples of usable metals or base alloy materials are Zinc, Aluminium, or Tin and preferably the coating is a zinc or zinc based coating. The material of the coating is selected so that it is non reactive with respect to the material of the spacer, and also so that it can be easily applied without detracting from or damaging the performance of the spacer.

The coating is preferably sprayed onto the inner face of the pipe in pipe spacer. There are several types of system for the application of such a coating, and in the present application the preferred method of application is a molten phase application. In the example of a zinc coating the coating may be applied at a temperature in the order of 420C and possibly as high as 475C.

In a particular embodiment of a pipe in pipe spacer according to the invention, the coating is sprayed to a thickness of between 0.1 and 0.3 mm.

In apreferred embodiment of the spacer according to the invention, the first pipe is an oil pipe and the second pipe is a carrier pipe.

In use the important aspect is that the differential in grip of the spacer between the first pipe (oil pipe) and the outer surface of the spacer with the second pipe (carrier pipe) is maximised in favour of the inner surface grip without causing or bringing about a failure of the spacer. Fulfilling of these criteria will mean that the spacer will stay securely in position when the first pipe is being located in the second pipe. However as we all know there are practical considerations which mean that the spacer is likely to be subj ected to a loading that in normal circumstances will cause it to move. The grip of the spacer to the inner pipe is the important factor in overcoming the tendency to move and maybe further enhanced by provision of a tightening means to mechanically pressure the spacer against the inner pipe and thereby enhance the tightness of this fit. The loading will have a in effect on the geometry of the spacer deforming the spacer to increase the surface area contact between the inner surface of the spacer and the first pipe. In one embodiment the tightening means comprises a conventional screw type device which applies a tightening force tangentially to the pipe cause the spacer to tighten about the pipe, enhancing the grip of the spacer to the pipe.

With regard to the loading that is applied it is important to note that the load that can be applied to the spacer is limited so that failure due too high a load of the spacer or the bolt does not result. The obj ect of the application of the load is to apply a force which deepens the interaction between the coated surface of the spacer and the surface of the pipe. The force applied should be sufficient to do this, and this may result in the spacer deforming in the vicinity of the contact with the pipe but that is acceptable if the grip is enhanced.

In a preferred embodiment of the spacer preferably the spacer is manufactured from a number of components which are assembled about the pipe and secured together. Preferably each of the components of the spacer to be secured together are substantially identical.

An embodiment of a pipe in pipe spacer will now be illustrated byway of description of an example as shown in the attached drawings, in which:

Figure 1 shows a side view of a spacer made in accordance with the present invention;

Figure 2 shows an end view of the spacer shown in Figure 1 ;

Figure 3 shows a cross sectional view of the tightening means of the spacer shown in Figure 1 ; and

Figure 4 shows a blown up side view, partly in cross section, of the spacer of Figure 1 Referring to the drawings there is shown a pipe in pipe spacer 10. The spacer 10 is made by casting nylon material and working this into the correct orientation.

The spacer 10 is generally tubular and comprises two substantially identical halve sections 1 OA, 1 OB each of which has an inner face 2 sized to contact and engage with the outer surface of an oil pipe (not shown); an outer surface 3 sized to fit engage the inner surface of a carrier pipe but be able to slide easily within said carrier pipe; and interconnecting means 4 provided at each end thereof to enable the two component halves to be located and fixed in relation to a pipe about which they are fixed.

The spacer 10 when fitted extends along and contacts a small portion of the length of the pipe to which it is fitted. Each of the spacer forms a discreet element so that insulation or other material maybe located in the space between the two pipes between the spacers. The spacer will act to maintain said material in location.

The interconnecting means 4 provided in each end of the spacer 10 comprises two through bores 5 having a countersunk section 6. When the spacer 10 is fitted about apipe, then interconnecting means 4 are aligned and abolt 7 is fitted through respective aligned bores. In the particular design shown, the interconnecting means 4 comprises two sets of two through bores and therefore four bolts are used to assemble and secure the spacer 10 about the pipe.

In typical offshore applications both the inner and outer pipes of apipe in pipe construction will be steel pipes, but this invention is not limited to use with these types of pipes alone. The coefficient of friction between the inner face of the cast nylon of the spacer and the outer surface of the steel oil pipe is therefore of the order of 0.3.

As will be appreciated by those skilled in the industry, there is therefore very little resistance for the spacer to move with respect to the pipe. Further, whilst the interconnecting means 4 can be tightened to enhance the grip of the spacer 10 with respect to the pipe there is still a tendency for the cast nylon spacer to move with respect to the pipe. Further the nature of the cast nylon material also limits the loading that can be applied by tightening of the bolts 7 of the interconnecting means 4.

Ih the present invention in order to enhance the grip of the spacer 10 to the pipe in use the inner face 2 of the pipe in pipe spacer 10 is coated with a thin layer 8 of zinc, typically to a thickness of approximately 0.2 mm. The coating maybe sprayed onto the inner surface of the pipe in pipe spacer 10. The coefficient of friction of between the coated inner face of the spacer and the outer spacer of the oil pipe thereby increased to the order of 0.6.

Further, in addition to the increase in the coefficient of friction, should the spacer 10 move, the loading is between the spacer 10 and the oil pipe is such that the coating material will deform and enhance the grip between the spacer 10 and the pipe.

In use the two halves of the spacer 10 are located about the pipe. The bolts 7 are inserted through the aligned through bores 5 , (four in total), and nuts fitted. The bolts 7 are tightened so that the spacer 10 bears against the pipe gripping the pipe.

A plurality of pipe spacers 10 are so fitted at predetermined intervals along the length of the oil pipe. The oil pipe with spacers is then pulled into a carrier pipe and the outer surface 3 of the spacer 10 bears against the inner surface of the carrier pipe. Because the coefficient of friction between the inside surface of the pipe in pipe spacer and the outer surface of the oil pipe is greater than the coefficient of friction between the outer surface of the pipe in pipe spacer and the inner surface of the carrier pipe, the oil pipe slides into the carrier pipe without axial displacement of the pipe in pipe spacers along the length of the carrier pipe.

Claims

1. A pipe in pipe spacer for use in the coaxial spacing of a first pipe within a second pipe, which pipe in pipe spacer has an inner face which contacts and engages with the outer surface of the first pipe, characterised in that the inside face of the pipe in pipe spacer is coated with a coating of a material so that the coefficient of friction between the outer surface of the first pipe and the inside face of the pipe in pipe spacer is higher than the coefficient of friction between the outer surface of the first pipe and the inside face of the uncoated pipe in pipe spacer.

2. A spacer according to claim 1 in which is a cast nylon spacer.

3. A spacer according to claim 1 or claim 2 which is coated with a metal or metal composite coating.

4. A spacer as claimed in claim 3 wherein the spacer is coated with zinc or aluminium or tin or an alloy of one or more of these materials.

5. A spacer according to claim 3 in which the coating is a zinc coating.

6. A spacer according to any of claims 1 to 4 in which the coating has been sprayed onto the inner face of the pipe in pipe spacer.

7. A spacer according to claim 5 in which the coating has been sprayed to a thickness of between 0.1 and 0.3 mm.

8. A spacer according to any of claims 1 to 6 in which the first pipe is an oil pipe and the second pipe is a carrier pipe.

9. A spacer as claimed in any preceding claim, which includes tightening means to mechanical pressure the spacer against the pipe.

10. A pipe in pipe spacer substantially as hereinbefore described and with reference to the accompanying Figures.